Schemas, Frames and Knowledge in Systems Development

1
Schemas, Frames and Knowledgein Systems
Development

• Lecture 9

2
Topics

• Prize giving
• Bus example answer
• Schemas, Frames, Pre-structuring
• A problem
• Kinds of systems
• Repository
• Simulation
• Decision support
• Next week Matching problems

3
Bus Display

• The enhanced model to handle time
• The simplest possible data model
• Relations and Business Objects
• Test-driven development
• Route as a Schema

4
The enhanced model
select from route natural join departure
natural join runperiod where dtime gt
current_time and current_date between startdate
and enddate
5
The simplest possible modelOccams Razor

• do the simplest thing possible to meet the
  requirements
• A single routeno identifies a route
• Code incorporates variations such as
• Direction
• In term/out of term
• New releases of timetables
• But no requirement to display such data, so dont
  model as separate attributes

6
Objects and relations

• route or Route ?
• The route base record
• Or the closure of route relations
• baserunperiodsdepartures
• Route is the Business object the unit of
  creation, retrieval and deletion
• Object-relational databases provide some support
  for Route as a Class
• Both the Relational and the Object-oriented data
  models impose a structure on the DoD

7
Automated Testing

• Test-driven development
• tests (input expected output) written BEFORE
  the code
• the code is written to make the tests work
• tests automated
• Tests run when a change is made regression
  testing
• In the example solution
• A test script sets up minute amount of data
• Each test defines the expected outcome
• Script can be run repeatedly until all tests pass
• Issues
• What kinds of system functionality can be tested
  this way?
• Should developers be responsible for devising
  their own tests?
• Can software be adequately tested?

8
Schema
Development
descriptive
What is a route?
schema
DoD
Use
prescriptive
A route is a
9
Schema in Use

• Schema has a fixed structure with a set of place
  holders to allow variation
• A slot for the single destination of all buses on
  the route
• So a route cant have multiple destinations
• But the last 70 goes to Muller Road Depot, not
  Centre
• So this will have to be a different route
• Or alter schema to allow over-ride destination in
  departure
• A Schema structures our perception of the world
• We change the schema when the fit is poor

10
Minskys Frames

• Marvin Minsky is one of the fathers of artificial
  intelligence
• When one encounters a new situation (or makes a
  substantial change in one's view of the present
  problem) one selects from memory a structure
  called a Frame. This is a remembered framework to
  be adapted to fit reality by changing details as
  necessary
• A frame is a data-structure for representing a
  stereotyped situation, like being in a certain
  kind of living room, or going to a child's
  birthday party. Attached to each frame are
  several kinds of information. Some of this
  information is about how to use the frame. Some
  is about what one can expect to happen next. Some
  is about what to do if these expectations are not
  confirmed.
• Thinking always begins with suggestive but
  imperfect plans and images these are
  progressively replaced by betterbut usually
  still imperfectideas.
• Marvin Minsky, A Framework for Representing
  Knowledge, MIT-AI Laboratory Memo 306, June, 1974

11
Gestalt psychology

• Gestalt form pattern shape organised whole
  or unit
• notion of pre-existing schemata, or
  organisational frameworks for structuring
  information, as opposed to perception built up
  from visual stimulus alone.
• In the case of visual perception, a schemata
  provides a framework within which external
  stimuli are sensible. A frogs visual and motor
  system is pre-programmed for fly-recognition

12
Design Studies

• Cognitive psychologists observe that for an
  experienced analyst designing a familiar object
  in a familiar domain, the overall task could be
  characterised as being dominated by the retrieval
  of previously-stored knowledge (Adelson and
  Soloway).
• Research by Curtis et al has shown the importance
  of domain knowledge in design, where domain
  knowledge entails understanding of the problems
  which occur in a specific application field and
  the tried and tested (and the failed) solutions.
• Brown and Chandrasekaran identify the strategy of
  'Design by Critiquing and Modifying Almost
  Correct Designs' as one of four main design
  processes (decomposition, design plans, and
  constraint solving are the others).

13
Pre-structuring

• Hillier, Musgrove and O'Sullivan suggest that
  building design is essentially a matter of
  prestructuring problems based on the designer's
  knowledge
• of solution types
• of the 'latencies of the instrumental set' (the
  raw materials time) in relation to solution
  types
• of informal 'codes' which relate problems to
  solution types
• it is not a matter of whether the problem is
  pre-structured but how it is pre-structured, and
  whether the designer is prepared to make this
  prestructuring the object of his critical
  attention
• Hillier Musgrove and OSullivan Knowledge and
  Design 1972

14
A Pattern Language

• Christopher Alexander and colleagues wrote an
  influential collection of 253 patterns for
  living good solutions to recurring problems in
  architecture.
• Language intended to provide a basis for
  community architecture
• Gamma et al picked up this work and applied it to
  the emerging area of Object-oriented Programming.
• Provides a language for developers to use within
  a project
• We need the Observer pattern here
• Pattern conferences develop a rich array of
  patterns encapsulating the experience of
  developers in many software and organisational
  contexts.

15
Jacksons Problem Frames

• An inability to discuss problems explicitly has
  been one of the most glaring deficiencies of
  software practice and theory. Again and again
  writers on development methods claim to offer an
  analysis of a problem when in fact they offer
  only an outline of the solution, leaving the
  problem unexplored and unexplained
• Jackson adopts a more formal, analytic approach
  to problem analysis and has identified a small
  number of Problem Frames. more in a later
  lecture

16
Problem Police Identity Parade

• See handout

17
What kind of System is it?

• a repository of data
• a model of a Domain of Discourse
• an advisor classifying, matching
• a co-ordinator of human activity
• a tool for the construction of an artefact
• a learning system
• .....
• Real systems have aspects of several kinds but it
  helps to focus of each viewpoint in turn, then
  integrate them divide and rule

18
Repository Frame

• Common to view an information as a simple
  repository of data.
• Data is collected, stored, kept safe from falling
  into the wrong hands, from being lost.
• Data can be extracted, reorganised, removed if no
  longer relevant
• Data should only be accepted if it conforms to
  rules for good data -integrity rules
• CRUD (Create, Retrieve, Update, Destroy)

19
Repository Frame (2)

• In the problem, we need to be able to
• store data about suspects and volunteers
• readily retrieve data when required
• keep the data secure from loss, or access by the
  wrong people
• Metaphor SYSTEM IS A BANK

20
Model Frame

• System contains a model of the domain of
  discourse
• Issues
• how much of the real world to model, in what
  detail to support needs of users, now and in the
  future?
• how to ensure that the model and the real world
  stay closely in synchrony - that changes to the
  real world (a volunteer moves house) are
  reflected in the model (address field updated)
  quickly and accurately

21
Model Frame

• Now we must consider the process by which the
  model and the domain are connected, as well as
  the way the model supports the users needs
• Jackson calls this the Information Display
  Frame
• E.g. a real-time bus information system how is
  the changing bus position reported and used to
  predict an arrival time
• Metaphor SYSTEM IS A MAP

22
Resource Manager Frame

• Allocation of scarce resources, such as
• seats on flights
• rooms for lectures
• beds for patients
• volunteers to identity parades
• Problem is to maximise utilisation of resources
  whilst minimising delay and inconvenience to
  parties
• Common Issues
• Granularity of resource units
• Handling time
• Modelling and visualising allocations
• Cancellation policy
• Over-booking policy
• Allocation policy - priorities, up-grading
• A common sub-problem is to match a clients needs
  to available resources

23
Matching Frame

• E.g. Shazam (2580)
• Matching typically involve
• two sets of individuals e.g.
• the sample of music / suspect - Requirement
• the database of tracks /volunteers - Resources
• adequate representations of both
• a fitness function which calculates how well
  matched a Requirement is to a Resource
• More on Matching next week

24
Frame Approach to Development

• Rough description of Problem
• Select suitable Frame(s) to fit Problem
• A well-fitting Frame provides
• standard terminology
• checklist of issues which need to be addressed,
  questions which need to be asked
• index of solutions to commonly occurring
  sub-problems
• Frame allows us to draw upon relevant prior
  knowledge of this problem type
• Identifying appropriate Frames is a Matching
  Problem!

25
Tutorial Questions

• Skim Read Minskys paper on Frames
• Identify aspects of the Identity Parade problem
  which map into these Frames
• Repository
• Model
• Resource Allocation
• Matching
• What analysis questions do these frames suggest?
• What is left out?

26
Related Reading

• Adelson, Beth and Soloway, Eliot, The Role of
  Domain Experience in Software Design, IEEE Trans.
  Soft. Eng. SE-11 Nov 1985 1351-1360
• David C. Brown and B. Chandrasekaren, Design
  Problem Solving Knowledge Structures and
  Control Strategies, Pitman 1989
• Eric Gamma, Richard Helm, Ralph Johnson and John
  Vlissides Design Patterns, Addison-Wesley 1994
• Bill Hillier, John Musgrove and Pat O'Sullivan
  Knowledge and Design in Developments in Design
  Methodology ed Nigel Cross Wiley 1984
• Michael Jackson Software Requirements and
  Specifications Addison-Wesley 1994
• Michael Jackson Problem Frames, Addison-Wesley
  2001
• Marvin Minsky, A framework for representing
  knowledge MIT 1974
• Peter Rowe, Design Thinking, MIT Press 1987